How can I add two values in a list in C++ using rbegin() and advance(iterator,1)?

I'm trying to calculate the fibonacci series using a list in C++, as instructed.
I was left with notes on how to improve it, and I simply don't understand what is being asked of me. How can i use rbegin() and advance(iterator,1) to add previous values and calculate a new one?

Here is what I had earlier.

list mutableFibonacci(int position)
{

list<int> series;
int first = 0; //Remove
int second = 1; //Remove

for (int i = 1; i <= position; i++)
{
if (i == 1)
series.push_back(1);
else
{
//We can get the last value and the value before from the series, like so, series.rbegin(); then get the value from the reverse iterator. Then we can call advance(iterator, 1) to get to the previous value. We can get the second to last value.
series.push_back(first + second);
first = second;
second = series.back();